|Previous Edition Warning: This article discusses a topic from a previous edition of Warhammer 40,000.|
Its canonicity is in question but was once considered canon.
An Adrenaline Sac is a Tyranid Biomorph. The sac is a special container for excess adrenaline which the creature can use to temporarily enhance its senses, abilities and physical attributes. It is not big enough for extended use and will run out and require refilling after a single use.